The present invention generally pertains to the field of electronic circuits. More particularly, embodiments of the present invention are related to a circuit for regulating a signal using autobias.
A conventional cathode ray tube (CRT) creates an image on a phosphor coated display screen by focusing a beam of electrons onto the screen and thus making the phosphors emit visible light. The electron beam is typically formed by first causing a cathode inside the vacuum of the CRT to emit electrons by applying a differential voltage between the cathode and a grid. The CRT has one or more anodes to attract, focus, and accelerate the electrons. Thus, the anodes may collimate the electrons into a tight beam hitting a spot of the display screen. By creating currents in coils outside the CRT, a magnetic field is created within the CRT to direct the electron beam at any desired spot of the display screen.
As the phosphors in a CRT respond to the intensity of the beam current, the brightness of the picture will be a function of the beam current. However, the beam current does not stay constant for a given cathode voltage over its lifetime. Hence, the picture intensity will typically change even though the same voltage is applied to the cathode. Thus, it is desirable to have a means to compensate to keep the CRT picture uniform over time.
Compensation systems have been proposed to reduce this problem. Some techniques are suitable for a DC coupled system, but not for an AC coupled system. Such a DC coupled system typically requires significant power and slows the response of the system relative to an AC coupled system.
Thus, a need exists for a technique for compensating for changes in picture intensity in a CRT due to aging on the CRT. A further need exists for a technique that does not consume considerable power. A still further need exists for a technique that does not change the time response of the system when varying the bias voltage. A still further need exists for a technique to be used in an AC coupled system.
The present invention provides a circuit and method for regulating a signal, such as a beam current in a cathode ray tube. Embodiments consume less power than some conventional techniques. Embodiments do not change system response time when varying the bias voltage as do some conventional techniques. Embodiments are suitable for a system in which the CRT is AC coupled to driver circuitry.
A regulating circuit and method are disclosed. The circuit may comprise an input stage for inputting a signal and for producing a sense signal based thereon. The input signal may be from a cathode ray tube. The circuit may have elements for inputting a plurality of timing signals including a first and a second timing signal. The circuit may have a first stage for comparing a first reference signal with the sense signal when the first timing signal indicates and for outputting a first correction signal based on the comparison. And the circuit may have a second stage for comparing a second reference signal with the sense signal when the second timing signal indicates and for outputting a second correction signal based on the comparison.
The circuit may further comprises elements for measuring a leakage signal in the input signal during a time interval defined by a third timing signal of the plurality of timing signals. In this embodiment, the first stage is further for subtracting the leakage signal from the sense signal prior to the comparison.
These and other advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.